On the first point, Firefox can store both logins and form auto-fill data. There are separate places to clear these.

(1) To remove a saved login (username and password), you can go to the Options dialog here:

"3-bar" menu button (or Tools menu) > Options > Security > "Saved Passwords" button

(2) To remove saved form entries, Firefox doesn't have a similar item-by-item dialog. Instead, you can:

• Clear individual form entries by using the down arrow on the keyboard to highlight them in the drop-down list that appears below the form field and press the Delete key or Shift+Delete.

• Clear ALL of your saved form entries for all sites using the Clear Recent History feature.

• Use an add-on like the following to delete specific form data for specific sites: https://addons.mozilla.org/firefox/addon/form-history-control/

On the second point, in the address bar (also called the location bar), do the items remaining after you clear history have a blue star? If so, those are bookmarked sites. If not, hmm, why are they still there? When you clear history, are you choosing the Time range "Everything" at the top of the dialog?

You can remove all data stored in Firefox from a specific domain via "Forget About This Site" in the right-click context menu of an history entry ("History > Show All History" or "View > Sidebar > History") or via the about:permissions page.

Using "Forget About This Site" will remove all data stored in Firefox from that domain like bookmarks, cookies, passwords, cache, history, and exceptions, so be cautious and if you have a password or other data from that domain that you do not want to lose then make sure to backup this data or make a note.

You can't recover from this 'forget' unless you have a backup of the involved files.

It doesn't have any lasting effect, so if you revisit such a 'forgotten' website then data from that website will be saved once again.